I haven't used Zotero in anger for a few years and can't get to my laptop right now to verify. But I used to rely on automatic exports to a folder that I sync'd elsewhere. Never used a paid Zotero subscription, never "self-hosted" it, and had many gigs of data (including PDF attachments) working fine for years.

I used "better bibtex" (?) to ensure files were reliably renamed and moved to an appropriate folder, all automatically.

A real set-and-forget setup that ran without hitch for years.

uh oh - didn't realize sync was paid (stupidly). apparently i am at 99.6% of the free tier

now i'm interested in the answer to your question - i have my own machine running 24/7 that i would love to use. i like the software enough that maybe i'd pay/donate